1. Field of the Invention
This invention relates to a processor, a memory for storing data utilized by the processor, a computer system including the processor and the memory, and a method for transferring the data in the computer system.
2. Description of the Related Art
Computers are incorporated in many products such as digital cameras, digital televisions, DVD players, DVD/HDD recorders, game machines, cellular phones, portable audio players, control units for vehicles, and the like. Such devices and systems, in which the computers are incorporated, process copyright protected contents. The devices and systems also deal with important information such as private information and accounting information.
Wrongful activities, which include unauthorized copy of contents after decryption, and acquisition of private information and interpolation of accounting information as running an unauthorized program, have become problems for the devices and the systems.
As a method for preventing the illegal acquisition of the data (including programs) by observing signals on bus connecting the processor and the memory, for example, Japanese Patent Application Laid-Open No. 2003-298569 discloses that the processor encrypts as writing data in the memory and processes, after reading the encrypted data from the memory, decrypts and processes. As such, since the encrypted data only flows in the bus connecting the processor and the memory, reading of the data is not possible without knowledge of a key for decrypting.
However, use of strong encryption, for example public key encryption, when encrypting the data, becomes necessary so as to prevent third party's cryptanalysis. Yet, such strong encryption requires higher processing cost for encrypting and decrypting and becomes an obstacle for an increase of the processing speed.